Method of washing a gelled thread of an acrylonitrile polymerization product



July 26, 1955 l. WIZON ET AL METHOD OF WASHING A GELLED THREAD OF AN ACRYLONITRILE POLYMERIZATION PRODUCT 2 Sheets-Sheet 1 Filed April 11, 1952 Q; INVENTORS //PV//V W/ZO/V, fRC/Vdl W. cuMM/A cs J/e BY mPn/u/P cprssu/zz A W K L A RNEY w ry .4. var

United States Patent METHOD 0F WASHING A GELLED THREAD OF AN ACRYLONITRILE POLYMERIZATION PRODUCT Irvin Wizon, Stamford, Percival W. Cummings, Jr., Cos Cob, and Arthur Cresswell, Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of .Maine Application April 11, 1952, Serial No. 281,938

r 2 Claims. (Cl. 8--151.1)

This invention relates to certain new and useful improvements in a method for treating, and more particularly washing, a wet-spun, gelled thread (including both monofilaments and multifilaments) of a synthetic material, specifically an acrylonitrile polymerization product.

In certain processes of manufacturing certain synthetic threads or yarns, it is frequently desirable to wash or otherwise treat the freshly spun thread in continuous length. One type of apparatus that has been used for this purpose involves a plurality of spaced, generally superimposed, thread-advancing reels upon each of which the thread progresses bodily along the length of the reel, in a generally helical path, from the point where it is wound thereupon to a discharge point, Where it is unwound from the reel and led to the next reel. An arrangernent of this kind and theuse of the apparatus in the production of viscose rayon is described in, for example, U. S. Patent 2,225,640. Another type of threadadvancing device that has been employed for the wet treatment or washing of continuous lengths of synthetic yarn comprises a pair of spaced, converging rolls about which the yarn is Wound and over which the yarn 'advances in a helical path from the feed-on end to the take-01f end. During the passage of the advancing helices or thread or yarn over the converging rolls, or plurality of converging rolls, the thread is treated with a liquid, for example by means of a jet through which the liquid is sprayed upon the roll and upon the thread advancing thereupon. Such apparatus and processes of treating a thread are described in, for example, Hartman et al. Patent 2,194,470 and Gram Patent 2,294,902.

The present invention, although not limited thereto, is especially concerned with certain new and useful improvements in a method of the kind involving the use of a pair of spaced, converging rolls. More particularly the invention relates to certain method improvements involving the use of such rolls and auxiliary equipment in Washing a wet-spun, gelled thread of an acrylonitrile polymerization product which has been produced as described in Cresswell Patents 2,558,730 and 2,558,731, in Cresswell and Wizon Patent 2,558,733 and in the copending application of Cresswell and Cummings, Serial No. 214,616, filed March 8, 1951.

The invention disclosed in the aforementioned Cresswell and Cresswell et al. patents involves the precipitation or coagulation of an acrylonitrile polymerization product in approximately its desired shape from a watercoagulable solution thereof, more particularly a concentrated aqueous salt solution of the kind disclosed by Rein in his Patent No. 2,140,921. The precipitation is efiected by contacting the aforesaid solution of a polymer or copolymer of acrylonitrile With a cold aqueous coagulant, more particularly water alone, at 'a temperature not substantially exceeding +10 C. This coagulant is a non-solvent for the acrylonitrile polymerization product but will dissolve the solvent in which the said product is dissolved. As is pointed out in these patents, it was found that by keeping the temperature of the aqueous coagulating bath at or below +10 C., e. g., within the range of --I15 C. to +10 C. and preferably at from about -.l5 C. to about +5 C., the precipitated gels in general are clear or substantially clear, tough, ductile and, in thread or other form, can be stretched to orient the molecules, thereby increasing the cohesiveness, tensile strength, toughness, resilience and otherwise improving the properties of the finished product.

In Cresswell Patent 2,558,731 and also in Cresswell et al. Patent 2,558,733 there are described a method and apparatus for washing a Wet-spun gelled thread of an acrylonitrile polymerization product, which thread has been produced in the manner above set forth and which is washed with a cold liquid medium comprising Water while the gelled fiber is moving in a helical path over a pair of spaced converging rolls, more particularly by applying cold water to the upper roll of a pair of spaced, converging wash rolls.

We have found that, in washing a wet-spun, gelled thread of a polymer or copolyrner of acrylonitrile that has been produced as described in the aforementioned Cresswell and Cresswell et al. patents, the bulk of the salt present in the freshly spun thread is rapidly extracted therefrom with a relatively small amount of wash liquid while the last portions are removed much more slowly and require the use of large volumes of wash water. The present invention takes advantage of this discovery and makes possible the separate collection of the first part of the wash efliuent, which is a relatively highly concentrated solution of the extracted salt and which solution can be economically concentrated and re-used in the process as a solvent for the acrylonitrile polymerization product or, at a lower concentration, as a coagulating bath. The invention also permits the separate collection of the more dilute wash eflluent which is uneconomical for concentration and re-use. The invention also makes possible an improved technique for separating the more valuable and more highly concentrated wash efiiuent from the dilute wash efiluent of no practical value.

In brief, the present invention has as its primary objects and provides an efiicient method for washing a wetspun, gelled thread of the aforementioned kind; and specifically it makes possible the more economical recovery of the salt retained in the thread and more ethcient washing to an optimum level of residual salt in the final washed thread or yarn, when spinning threads of various deniers at varying rates of speed, than is provided by the method and apparatus described in Cresswell Patent 2,558,731 and Cresswell et :al. Patent 2,558,733.

The novel features which .are characteristic of our invention are set forth in the appended claims. The invention itself, however, will best be understood by reference to the following more detailed description when considered in connection with the accompanying drawing in which Fig. 1 is a somewhat diagrammatic side elevation of apparatus embodying the present invention and illustrative thereof; Fig. 2 is can end view'of the apparatus shown in Fig. l; and Fig. 3 is a graph showing the results of washingagelled thread of an acrylonitrile polymerization product in accordance with the instant invention.

The wet-spun, gelled threads which .are washed in accordance with our invention are preferably those which are made either from .homopolymeric acrylonitrile or from acrylonitrile copolymers containing a major proportion by weight of combined acrylonitrile, and especiallly those copolymers which contain in the molecules thereof an average of at least about .by weight of combined acrylonitrile. These acrylonitrile polymerization products are prepared by methods well known to those skilled in the art. We prefer to use polymeric and copolymeric acrylonitriles having an average molecular weight within the range of about 15,000 to about 300,000, more particularly about 40,000 or 50,000 to about 150,- 000 or 200,000, and still more particularly those having an average molecular weight within the range of about 60,000 to 90,000, as calculated from viscosity measurements, using the Staudingerequation (reference: U. S. Patent 2,404,713).

Illustrative examples of monomers which can be copolymerized with acrylonitrile to yield a copolymer containing a major proportion by weight of combined acrylonitrile are compounds containing a single CH2=C grouping, for instance the vinyl esters (e. g., vinyl acetate, etc.), the acrylic esters (e. g., methyl acrylate, etc.), acrylamide, vinylpyridine, methacrylonitrile and others of the kind mentioned in the aforementioned Cresswell and Cresswell et al. patents and in Cresswell et al. copending application Serial No. 214,616.

The preferred wet-spun thread which is treated, specifically washed, in accordance with the present invention is one yvhich has been prepared in the'manner described in the aforesaid Cresswell et a1. copending application and which involves extruding an aqueous solution of an acrylonitrile polymerization product containing a major proportion by weight of combined acrylonitrile through a shaped orifice into aliquid coagulating bath comprising an aqueous solution containing from about 3% to about 25%, by weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature not exceeding +10 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of the same water-soluble thiocyanate which is a component of the said liquid coagulating bath.

With reference to the accompanying drawing a wetspun, gelled thread 10 of an acrylonitrile polymerization product is led from a coagulating bath of the kind briefly described in the foregoing paragraph and more fully in the aforementioned Cresswell et a1. copending application Serial No. 214,616 to a suitable thread-storage, thread-advancing device 12. In such a device the thread is caused to move through a helical path having a multi* plicity of turns the axis of which is at an angle to the horizontal and in which the thread moves from the feedon end to the take-off end of the said path. This device advantageously may take the form shown by way of illustration in Figs. 1 and 2 of the accompanying drawing. The device there shown comprises converging, liquid-treating or wash rolls, and more particularly an upper roll 14 and a lower roll 16. These rolls are positively driven by a suitable driving mechanism. They may be driven at the same peripheral speed from a common drive; or, as illustrated in the drawing for purpose of simplicity, individual driving mechanisms 18 and 20 may be provided for driving upper roll 14 and lower roll 16 at the same peripheral speed. Rolls 14 and 16 are suitably spaced from each other, e. g., 4, 6, 8 inches or more, and preferably are suspended in the same vertical plane. They converge slightly toward each other at the delivery or take-off end, which convergency has been somewhat exaggerated for purpose of clarity in the drawing. For example, with rolls 4" in diameter, 13 long and on 7" centers at the back (feed-on end), an angle of convergency of 3 l' at the take-off end has been used satisfactorily. The rolls may be inclined, if desired, at an angle from the horizontal. Either of these rolls, if desired, may be normal to the horizontal. The diameter and length of the T011814 and l may be varied as desired or as conditions may require, but ordinarily they are such that, during operation, the length of thread being washed, while continuously moving in a helical path,

is from about yards to about 40 yards, or even as much as 60 to 80 yards or more.

a 'The rolls 14 and 16 may be made of any suitable materialsuch, for example, as Monel metal, stainless steel,

chromium-plated copper, chromium-plated steel, fused quartz, glass, etc. The rolls are preferably formed of a material which is resistant to the corrosive attack of the thiocyanate solution and are provided with a relatively smooth surface. The surface of the roll, however, should not be so highly polished that difiiculty is encountered in the spacing of the helices of the thread as it advances over the surfaces of the rolls.

As the gelled thread 10 advances from the feed-on end toward the take-off end of the rolls, a liquid medium at a temperature not exceeding +10 C. and comprising an aqueous solution containing from about 3% to about 25%, more particularly from about 5% to about 15%, by weight, of the same water-soluble thiocyanate used as the coagulatingbath in forming the wet-spun thread 10 is applied through the spray or jet 22 to the feed-on end of the upper roll 14, whereby the thread at or near the point where it comes onto the roll and, also, the helices of thread adjacent to the feed-on end are washed with this cold, liquid wash medium, which is preferably at a temperature not exceeding -|-5 C., e. g., 0-2 C. As the thread advances along the rolls a spray of cold water is applied through the jet 24 to the middle portion of the upper roll 14. The wash liquids applied through the jets 22 and 24 are collected in the collecting trough 26 which is suitably positioned beneath the upper roll 14. This trough fits closely to, but does not touch, the lower surface of the roll and within the helices of thread advancing along the roll, so that the major amount of wash liquid flowing onto the roll through the jets 22 and 24 is collected within this trough and without any splashing of this liquid onto the lower roll. The effluent which is collected in the trough 26 drains out of the trough through the conduit 28 and thence is led to a suitable vessel for subsequent concentration and re-use in the process as has been briefly described hereinbefore.

The advancing helices of thread are next washed with water as they approach the take-off end of their helical path, which water is at a temperature higher than the temperature of the water used in the preceding washing stage and is preferably unheated, for instance at a temperature not exceeding 35 C. This water (at a temperature of, for example, 15 to 30 C.) is applied to the lower roll, beyond the point on the upper roll where the colder water is applied, through the spray or jet 30. The water applied to the lower roll through this jet is collected in the front end 32 of the collecting trough 34 which is divided in its bottom, that is, the bottom of the trough is discontinuous (see Fig. 4). Hence the efiluent collected in the front end 32 can be withdrawn through the conduit 36 and'thence discarded, since the concentration of thiocyanate in this effluent is so low as to make uneconomical the concentration or recovery of the small amount of thiocyanate therein.

As the thread advances over the rolls 14- and 16 some wash fluid is carried by the helices of thread and drips into the rear end 38 of the trough 34. This etlluent is withdrawn through the conduit 40 and combined with the efiluent which has been withdrawn from the collecting trough 26 through the conduit 28.

A barrier 42 is suitably positioned beneath the lower roll 16 for preventing the free intermingling, on the bottom surface of this lower roll, of the liquid applied to the front end of the lower roll with any liquid which is carried by the previously washed thread to the lower roll and retained on the bottom surface thereof. This barrier 42 may be of any suitable construction which will effect this result without causing any damage to the thread advancing along the roll. For example, it may take the form of a felt wiper 44 which is formed of wool or other suitable soft material and is held by the support 46, which may be clamped or otherwise attached to the trough.

The washed thread is then further processed, for instance in the manner described in the aforementioned Cresswell et a1. Patent 2,558,733.

. fr thefcllowingeztemples thepe seateseslar by weight.

Enamgzle J This exerrh e l u t u s the results bta ned hen cold wa e alcne 's applied to the uppe oll o a. pa r o spaced, conversing ash rql sv The gelled thread or yarn used in this example was P d item a spinning s lutio containing 7% of a copolymer (made by polymerizing a mixture of 95% acrylonitrile and methyl aerylate) dissolved in an aque u i elu ion cont ni g 2% of c um thiccyan te- The copolymer so a. l.

a 40 hol -.90 i rcu spiuoere rat aq s coa ula ins ath onta n ng 297 ca cium h neya and ra sed at a tempe ature sl ghtly be ow it C- eries f o ser ation were t ade t e rft 1$i series wit a ba imm rsio of .1.9. meter an h een r e with a ba h mmers on of .0 95 meter 'I-h :tres y hun-threa a ed item the e agul s b rth e e sp d. sen er in was te l Wh l we e per ted speeds correspon ins 0. 40 and meters per: t na take-up speeds in order to obtain a wide range .of washing times. A sp ay o te W e s pp ed to s antially he whole length of the upper roll at a flow rate of son per minute. Samples oi the thread were taken from the wash rolls at various stages of wash' and the residual content .of calcium thiocyanate was determined.

The results oi these tests indicate that most of the washing is accomplished, that is, most of the residual calcium thiocyanate is removed from the thread, in -the first seconds of time that the gelled thread is on the wash rolls. In this period of time the content of calcium thiocyanate was reduced to about 3.75%, based on the bone dry weight of the thread. With an additional washing time of seconds the calcium thiocyanate content of the thread was reduced to 1.2%, while a further increase of 50 seconds in the washing time reduced the calcium thiocyanate content to 1%. Additional washing with ice water was relatively ineffective, since a total washing time of 400 seconds reduced the residual content of calcium thiocyanate to only 0.75%.

Example 2 In this example the same copolymer solution used in Example 1 was extruded through a 40 holemicron spinneret into a coagulating bath containing about 10% of calcium thiocyanate and maintained at a temperature slightly below 0 C. Instead of washing the gelled thread on the washing rolls with ice water as in Example 1, the thread was washed with cold calcium thiocyanate solution of the same kind and concentration as that which constituted the coagulating bath by applying a spray thereof to substantially the whole length of the upper roll. In one series of tests the flow rate of the wash liquid was increased from 600 ml. per minute to 1300 ml. per minute. Samples were taken from the wash rolls at various points and the residual content of calcium thiocyanate was determined as in Example 1.

The results of these tests indicated that the largest proportion of the extractable calcium thiocyanate is removed from the thread in about 25 seconds and that a practical equilibrium is obtained after a total washing time on the rolls of about seconds. No practical advantages were gained in the extraction of the calcium thiocyanate from the thread when the flow rate of the wash liquid was increased from 600 ml. per minute to 1300 ml. per minute.

Example 3 This example illustrates the results obtained when washing technique and apparatus are employed in accordance with the present invention, and specifically in the manner illustrated in Figs. 1, 2 and 4.

The gelled thread used in this example was obtained by extruding a solution containing 9.5% of an acrylonitrite-methyl acrylate copolymer (produced by polymer- 6' izing mix u e o 2.5% acryloni il an 5% m thyl aeryla di ol ed n a 50% aqueo s so u i n Qt odium. thiocyanate. The copolymer solution vwas extruded th ugh a 49 h lemicron sp nn re nt an q e us coag lati g -bath ecn e' n ns abou 10% 9 sod um i cyanate and main in d a a per ure sli y ess ,thanfl C- The thread or yarn, after having been formed in the coagulating bath, was led over .a pair of spaced, converg'ing rolls over which it advanced in helical form. The yarn was washed on the upper roll in two stages as shown in Fig, 2, the first stage consisting of cold sodium thiocyanate solution at substantially the same temperature and of the same concentration as that which .constituted the coagulating bath. This was applied to the upper roll at the rate of 860 ml. per minute. The second stage comprised the application of deionized water, chilled to 1.5 C., to the upper roll only at the rate of 180 ml. per minute. The combined efiiuents from the upper roll were collected in a trough beneath the roll and thence led to a suitable storage vessel. It can be economically concentrated and re-used in the spinning P oce The third stage wash consisted of water along at a temperature of about 20 C. It was applied to the lower rojll only, as shown in Fig. 2,, at the rate of 620 ml. per minute. The eflluent from this roll was collected and discarded, since it was too dilute for eflicient recovery of the sodium thiocyanate.

Th spray s in w sh stag 1. 2 and 3 w re. re spee i y, 3 i h s a /.2 nches in length- The spray jets were Aa-inch tubes with -inch holes on A-inch centers.

The washed thread was sampled by collecting from the rolls at predetermined intervals, and the samples were then analyzed for residual sodium thiocyanate. The results are shown graphically in Fig. 3.

From the foregoing description and accompanying drawing, and especially from the graph, it will be seen that the present invention provides an improved continuous method of washing a wet-spun, gelled thread of an acrylonitrile polymerization product to remove residual thiocyanate, and also an improved and novel means for segregating the more valuable from the less valuable efiluents. As a result, the more highly concentrated thiocyanate effiuent can be economically concentrated and re-used in the process, with obvious practical advantages.

We claim:

1. A method of washing a wet-spun gelled thread of an acrylonitrile polymerization product which has been produced by extruding a solution of said polymerization product through a spinneret into a liquid coagulating bath comprising an aqueous solution containing from about 3% to about 25%, by weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature not exceeding +10 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of the same water-soluble thiocyanate which is a component of the said liquid coagulating bath, said method comprising passing the said thread through a helical path having a multiplicity of turns the axis of which is at an angle to the horizontal and in which the thread moves from the feed-on end to the take-off end of the said path; washing the continuously moving thread at the feed-on end of the said helical path and also the helices of thread adjacent to said feed-on end by applying thereto a liquid medium at a temperature not exceeding +10 C. and comprising an aqueous solution containing from about 3% to about 25%, by weight, of the same water-soluble thiocyanate used in the aforementioned liquid coagulating bath; next washing the advancing helices of thread with water at a temperature not higher than +10 C.; and finally washing the advancing helices of thread as they approach the take-off end of their helical path with water at a temperature higher than the temperature of the water used in the preceding washing stage.

2. A method of washing a wet-spun gelled thread of an acrylonitrile polymerization product which has been produced by extruding a solution of said polymerization product through a spinneret into a liquid coagulating bath comprising an aqueous solution containing from about 5% to about 15%, by weight, of sodium thiocyanate, said coagulating bath being at a temperature not exceeding +5 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of sodium thiocyanate, said method comprising passing the said thread through a helical path having a multiplicity of turns by feeding the thread to the feed-on end of a pair of spaced, cylindrical, wash rolls which are suspended in the same vertical plane, which converge slightly toward each other at the take-off end, which are revolving at the same peripheral speed and about both of which the thread is looped; washing the advancing helices of thread at the feed-n end of the said helical path and also the helices of thread adjacent to said feedon end by applying to the inner end of the upper of the said pair of wash rolls a liquid medium at a temperature not exceeding C., and comprising an aqueous solution containing from about 5% to about 15%, by weight, of sodium thiocyanate; next washing the advancing helices of thread by applying water to the middle portion of the upper of the said pair of wash rolls, said water being at a temperature not higher than +5 C.; and finally washing the advancing helices of thread as they approach the take-off end of their helical path by applying water to the outer end of the lower of the said pair of wash rolls, said water being at a temperature higher than the temperature of the water used in the preceding washing stage but not exceeding C. and being applied at a point on the lower roll beyond the point on the upper roll where the colder water is applied.

References Cited in the file of this patent UNITED STATES PATENTS 2,129,274 Hartmann et a1. Sept. 6, 1938 2,254,251 Uytenbogaart Sept. 2, 1941 2,272,182 Burkholder et al. Feb. 10, 1942 2,319,812 Gram May 25, 1943 2,356,767 Kropa Aug. 29, 1944 2,416,535 Naumann Feb. 25, 1947 2,476,757 Naumann July 19, 1949 2,558,731 Cresswell July 3, 1951 2,558,732 7 Cresswell July 3, 1951 2,558,733 Cresswell July 3, 1951 2,558,734 Cresswell July 3, 1951 2,572,268 Kuljian Oct. 23, 1951 2,573,578 Kuljian Oct. 30, 1951 2,690,405 Lowe Sept. 28, 1954 FOREIGN PATENTS 985,684 France Mar. 14, 1951 OTHER REFERENCES Journal of Textile Institute Proceedings, pp. P6P20, Jan. 1948. 

1. A METHOD OF WASHING A WET-SPUN GELLED THREAD OF AN ACRYLONTRILE POLYMERIZATION PRODUCT WHICH HAS BEEN PRODUCED BY EXTRUCING A SOLUTION OF SAID POLYMERIZATION PRODUCT THROUGH A PINNERET INTO A LIQUID COAGULATING BATH COMPRISING AN AQUEOUS SOLUTION OF CONTAINING FROM ABOUT 3% TO ABOUT 25%, BY WEIIGHT, OF A WATER-SOLUBLE THIOCYANATE WHICH YIELDS HIGHLY HYDRATED IONS IN AN AQUEOUS SOLUTION, SAID COAGULATING BATH BEING AT A TEMPERATURE NOT EXCEEDING +10*C. AND SAID ACRYLONTRILE POLYMERIZATION PRODUCTS BEING DISSOLVED IN A CONCENTRATED AQUEOUS SOLUTION OF THE SAME WATER-SOLUBLE THIOCYANATE WHICH IS A COMPONENT OF THE SAID LIQUID COAGULATING BATH SAID METHOD COMPRISING PASSING THE SAID THREAD THROUGH A HELICAL PATH HAVING A MULTIPLICITY OF TURNS TO AXIS OF WHICH IS AT AN ANGLE TO THE HORIZONTAL AND IN WHICH THE THREAD MOVES FROM THE FEED-ON END TO THE TAKE-OFF END OF THE SAID PATH; WASHING THE CONTINUOUSLY MOVING THREAD AT THE FEED-ON END OF THE SAID HELICAL PATH AND ALSO THE HELICES OF THREAD ADJACENT TO SAID FEED-ON END BY APPLYING ING THERETO A LIQUID MEDIUM AT A TEMPERATURE NOT EXCEEDING +10*C. AND COMPRISING AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 3% TO ABOUT 25% BY WEIGHT, OF THE SAME WATER-SOLUBLE THICOYANATE USED IN THE AFOREMENTIONED LIQUID COAGULATING BATH; NEXT WASHING THE ADVANCING HELICES OF THREAD WITH WATER AT A TEMPERATURE NOT HEIGHER THAN +10*C., AND FINALLY WASHING THE ADVANCING HELICES OF THREAD AS THEY SPPROACH THE TAKE-OFF END OF THEIR HELICAL PATH WITH WATER AT A TEMPERATURE HIGHER THAN THE TEMPERATURE OF THE WATER USED IN THE PRECEDING WASHING STAGE. 